Gamma-butyrolactone is of important chemical significance as the basis for a large number of syntheses. For instance, it plays a role in the manufacture of butyric acid and its derivatives, 1,4-butanediol, tetrahydrofurane, N-methylpyrrolidone, polyvinylpyrrolidone, methionine and so forth. Gamma-butyrolactone is also an important solvent among other things for acrylates and styrol-based polymers. It can additionally be employed among other things in the manufacture of synthetic fibers.
A series of manufacturing processes start from maleic anhydride or derivatives such as maleic acid, succinic anhydride or maleate, which are subjected to hydrogenation. Hydrogenation is usually conducted in the vapor phase and in the presence of catalysts. In the patent literature a large number of catalysts are described for this reaction. For example, U.S. Pat. No. 3,065,243 mentions a process in which copper chromite acts as a catalyst. As can be gathered from the description and the examples in this patent specification, large quantities of succinic anhydride are still produced in this conversion which must be recirculated.
There has been no lack of attempts to develop catalysts to improve the yield and the selectivity. Another goal of the experimentation was to improve the lifetime of the catalysts since their useful lifetimes in continuous operation are too short: the catalyst deactivates too soon.
Thus, the Canadian patent specification 840 452 describes more advanced catalysts formed on the basis of copper/zinc. These can be processed together with asbestos into suitable catalyst particles. Neither the catalyst claimed in this Canadian patent specification nor the comparatively produced copper chromite-asbestos catalyst can yet fulfill all demands made on a good catalyst for the manufacture of gamma-butyrolactone.
DE-OS 24 04 493 describes a process in which the hydrogenation is performed in the presence of water vapor. This is intended to reduce the coking of the catalyst. One disadvantage of this process is the fact that additional water is introduced, although water is produced as a by-product in any case, which makes this process more expensive.
Other copper chromite-based catalysts are described for example in U.S. Pat. No. 4,006,165, where this catalyst also has to contain nickel. These catalysts can be applied to aluminum oxide or silica such as kieselgur or be produced by mixing with these substances. EP-A1-0 638 565 describes a process in which gamma-butyrolactone is produced by catalytic hydrogenation of maleic anhydride in the vapor phase in the presence of catalysts based on copper chromite in reduced form. Although high selectivity and a good yield are achieved with the uniform, i.e. homogeneous catalyst based on the three components copper oxide, chromium oxide and silicon di-oxide, it appeared that the long-term capacity of the catalyst still leaves a lot to be desired.
U.S. Pat. No. 5,347,021 describes a process for manufacturing gamma-butyrolactone in which hydrogen and maleic anhydride are converted in the presence of a catalyst, again in the vapor phase. The catalyst is formed on the basis of the components copper oxide, zinc oxide, aluminum oxide and graphite. Although this process operates with comparatively good selectivity and a good yield, the catalyst has to be reactivated after this process has been running for about 100 hours.
Although a large number of catalysts for converting hydrogen and maleic anhydride into gamma-butyrolactone have already been described, there is still the need for catalysts with which this conversion can be conducted in a better, more advantageous manner.